Pseudoscientists
claim to base their theories on empirical evidence, and they may even
use some scientific methods, though often their understanding of a
controlled experiment is inadequate. Many pseudoscientists relish
being able to point out the consistency of their theories with known
facts or with predicted consequences, but they do not recognize that
such consistency is not proof of anything. It is a necessary condition
but not a sufficient condition that a good scientific theory be
consistent with the facts. A theory which is contradicted by the facts
is obviously not a very good scientific theory, but a theory which is
consistent with the facts is not necessarily a good theory. For
example, "the truth of the hypothesis that plague is due to evil
spirits is not established by the correctness of the deduction that
you can avoid the disease by keeping out of the reach of the evil
spirits" (Beveridge 1957, 118).